Previous investigations by us and others have used a cell culture system to establish the vascular function of TN. We have now extended these observations in vivo to test the hypothesis that the genetic deletion of TN in the apo E-/- background might modify neointimal hyperplasia in an injured artery, and in atherosclerotic lesions. TN/E-mice developed atherosclerotic lesions one-week after being fed on a high fat diet. This lesion development was more rapid and more complex than was observed with Apo E mice. Concomitantly, VCAM- 1 expression was detected in the TN/E group alone. FACS analysis revealed that the VCAM-1 expression level in TN/E-derived endothelial cells was markedly higher than that from apo E mice. Finally, TN was found to down-regulate VCAM-1 promoter activity when induced by TNF-a in endothelial cells. These data suggest that TN deficiency promotes leukocyte/endothelial cell interaction. In addition to the rapid development of plaque, chronic hyperlipidemia in TN/E mice resulted in the formation of unstable plaques. The antibody array and ELISA analyses of chronic hyperlipidemic plasma from the two mouse genotypes showed that eotaxin, a CC chemokine, is selectively upregulated by 4- to 5-fold in the TN/E groups when compared to apo E mice. Furthermore, there was an accumulation of mast cells in the adventitia of unstable lesions in TN/E group. Collectively, our data point to an anti-inflammatory role for TN in vascular diseases. The overall goal of this proposal is to test 4 specific hypotheses (Aims). - Aim 1. A specific domain/segment of TN negatively regulates TNF-a induced VCAM-1 promoter activity. Aim 2. Chronic hyperlipidemia in TN/E mice up-regulates eotaxin promoting an accumulation of mast cells. Aim 3. TN deficiency promotes neointimal formation after vascular injury. Aim 4. TN deficiency per se is sufficient for neointimal formation.